Fuel flow warning device



June 1o, 19475 J VOLIAZZO EN; 2,421,768

FUEL FLOW WARNING DEVICE Filed June 29, 41945 3 Sheets-Sheet l 6- lr511----1 Z5 2 wie. s.. 2

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J. VOLIAZZO EI'AL FUEL FLow WARNING DEVICE Filed June 29, 1945 3Sheets-Sheet 2 SYM z 5 g um 77 9 /c/ 6 n 85 Y 46 "ri "ri" roknvl/r Jun1o, 1947.

vJ. VLIAZZO I'AL I FUEL FLOW WARNING DEVICE Filed June 29, 1945 3`Sheets-Sheet 3 P Abe/m14 How Patented June 10, 1947 FUEL FLOW WARNINGDEVICE Jesse Voliaxso, Thomasville, Ga., and Vincent Medveckus, Venice,Flai Application June zs, 1945, serial No. 602,244

(Grlnted under the act of March 3, 1883, as amended April 30, 1928; 3700. G. 757) 9 Claims.

The invention described herein may be manufactured and used by or forthe Government for governmental purposes, without the payment to us ofany royalty thereon.

This invention relates to a fuel flow warning device for use with anaircraft engine fuel system to give adequate warning of fuel systemfailure.

Typical aircraft fuel system circuits include a fuel-pressure gage and afuel-pressure drop warning signal, with actuating mechanisms varied tofuel pressure on one side and to carburetor air pressure on the otherside, to give a continuous indication of the functioning of the system.'Ihese indicators. being responsive only or injector, do not giveadequate warning of fuel system failure due to conditions ormalfunctioning not proximately affecting the fuel pressure on the highpressure side of the fuel pump. Since the conventional fuel pump isdesigned to deliver the required volume of fuel to the carburetor orinjector at a constant discharge pressure under all conditions and for aconsiderable period after exhaustion of fuel at the supply tank, thefuel pressure is independent of the fuel flow rate and remains unchangedregardless of variations in the fuel flow. Hence. variations in fuelflow disproportionate to the requirements of the system for normalengine operation, such as results from leaks in the pressure side of thesystem or malfunctioning of the carburetor or, injector, may occur andexist for some time without change in fuel pressure and with noindication thereof by either the fuel-pressure gage or the fuel-pressurewarning signal.

When such equipped fuel systems malfunction under extreme operatingconditions, the operator of the aircraft is without any warning orpreindication of fuel system failure intime suilicient to takecorrective action to prevent engine failure. The correction period (i.e., the time interval between the warning signal and the actual failureof the system from fuel exhaustion or other malfunctions) afforded bythe fuelpressure gage and warning signal lamp of the conventional fuelsystem is approximately thirty seconds or less dependent upon the rateof fuel consumption of the engine at the time of the signal warning. Attimes, engine failure may occur practically upon signal warning as insystems with carburetors which require continuous pressure to dischargethe fuel and which cut out Another object of the invention is toprovidel a warning device for engine fuel systems in which the rate offuel flow in the system is compared with the fuel flow-rate necessary tomeet the fuel consumption requirements of the engine for differentnormal conditions of engine-operation and which will give adequatewarning of fuel flow in excess of and below the required flow-rate.

A further object of the invention is to provide a fuel flow warningdevice which is readily adaptable to all types of fuel pressure systemsand which also can be co-ordinated with the fuelpressure gage andpressure drop warning signal, or other safety complements, of aircraftfuel systems for reducing the hazards of fuel system failures andproviding additional safety in the operation of aircraft.

The objects andadvantages of the invention are attained by the novelconstruction and incorporation in an engine fuel-feeding system of afuel ow'waming device which, briefly described, comprises opposedforce-exerting means, one of which is responsive to mass air flow to theengine to exert a force which is a reference or measure of the requirednate of fuel flow to the engine for a, given engine speed and the otherof which is responsive to the fuel flow pressure in the pump inductionside of the system for exerting a force which is a reference or measureoi' the instant rate of fuel flow to the pump, in combination with afuel flow indicator including a movable member operatively connectedwith the opposed force-exerting means to be maintained in a givenposition indicative of a normal fuel flow when the opposed forces areequal and to be deiiected to positions at relatively opposite sides ofthe given position in accordance with an unbalanced relationship betweenthe forces resulting from supernormal or subnormal fuel flow.

A practical embodiment of the invention is illustrated in theaccompanying drawings,

quickly after the initial drop in fuel pressure. I5 wherein:

Figure 1 is a top plan view of the signal-control unit of the invention.Y

Figure 2 is a vertical longitudinal sectional view of the signal-controlunit housing and associated mechanism taken on line 2-2 of Figure 1.

Figure 3 is a vertical transverse sectional view on line 3-3 of Figure1.

Figure 4 is a schematic view of the essential units and circuits of atypical single engine airplane fuel system with the device of theinvention incorporated therein.

Figure 5 is a schematic view of the fuel system and signal-controlunitoinstallation illustrating the reaction of the unit to fuel systemfailure characterized by decreased fuel flow.

Figure 6 is a schematic View similar to Figure 5 but illustratingsignal-control unitV reactance t fuel system failure characterized byexcessive fuel flow.

Figure 7 is a detail sectional view of the signal unit.

Figure 8 is a top plan'view of the'signal unit.

'I'he fuel flow warning device of the invention comprises essentially asignal-control unit A and a signal unit B. 'I'he mechanism of thesignalcontrol unit A is housed within a body having an air section and afuel section separated by an intervening wall or partition I. In theconstruction shown in Figures 1 to 3 inclusive, the air section isdefined by a comparatively shallowcup-shaped body portion 2 and a highdome or cover 3 with bottom flange 4 supported on and fastened inleak-proof relation with the upper edge of the body portion 2, as byscrews 5, vwhereas the fuel section is defined by a lateral tubular bodyportion 6 forming a fuel conduit offset from and depending below thebottom wall 1 of the air section; the end portions 8 and 9 at the inletand outlet ends of the fuel conduit being reduced in diameter andexternally screw-threaded as shown for connection into s, fuel systemcircuit.

The air section is divided into two chambers by a pressure-sensitivebellows I0 contained within the domed cover 3; the space II on theinside of the bellows forming one chamber and the space I2 outside ofthe bellows forming the other chamber. A vent I3 for the chamber II isprovided in a stem I4 at the upper end of the bellows, and a vent I forthe chamber I2 is provided in the top of the cover 3. The bellows-stemI4 has an externally screw threaded portion I6 which protrudes through anon-threaded orifice in the top of the cover 3. A nut I'I carried by thestem I4 and in abutment with the top surface of the cover supports thestem and bellows in suspension within the chamber I2; contact betweenthe cover and the nut being maintained by the downward thrust of abellows-tensioning spring I8 encircling the stem I4 and in compressionbetween the top of the bellows and the overhanging underside of thecover. A lock nut I9 is also provided on the stem I4. The force exertedby the bellows in response to a pressure difference between chambers I Iand I 2 is applied to a movable member 2|! through a suitable medium 2i.In the construction shown, the member 20 is a horizontally disposedswitch arm of a lamp-circuit switch mechanism housed within the bodyportion 2 in spaced relation to the overhanglng bottom of the bellows,and the medium 2I is a helical spring extending vertically between theswitch arm and the bottomof the bellows with its lower end secured by akeeper 22 on the switch arm and its upper end secured by a keeper 23 onthe bellows. Adjustment and regulation of the initial tension 4 on thespring 2l is obtained by raising or lowering the bellows and this iseifected by proper turning chamber being such as to provide slightclearance 21 at the periphery of the impeller when the latter is in aplane perpendicular to the axis of the impeller chamber. The impeller isattached at 2| to a shaft 25 Journaled in a cross-bore lILat the top ofthe impeller chamber; the shaft extending into the air section andcarrying a cam 3| engazed with the underside 0f the switch arm 2U. Thecross-bore is open to the impeller chamber through an orifice l2 andleakage at the inner or air section end of the cross-bore is preventedby a suitable shaft seal 33. A spring 34 encircles the shaft at itsouter end and is housed within an enlargement 35 of the cross-bore withone end seated on the bottom of the housing and its other end engaging astop 38 on the shaft. 'I'he spring housing 3'5 is provided with a.screw-threaded closure plug 31. Flow of fuel through the impeller isprovided for by one or more ports in the central portion of the impellerand smaller ports or bleed openings 38 between the rim and centralportion of the impeller. Passage of fuel through the ports 38 iscontrolled by a, valve 40 connected with the impeller and loaded by avalve closing spring 4 I.

The impeller, shaft, and cam provide means for exerting a force on theswitch arm 20 in opposition to the force exerted on the latter by the i.with the extent of movement or displacement of the impeller about itsaxis inresponse to flow conditions in the uid of the impeller chamber.

The signal unit B, shown in Figures 4 and 7, comprises a lamp housing 42divided into concentric inner and outer lamp chambers 4I and 44; theformer having a red cover glass 45 bearing the legend No flow and thelatter having a green cover glass 46 bearing the legend Excessive flow.The central and smaller chamber 43 houses a single electric lamp 4l. Apair of similar lamps 48 and 48a are housed within the outer and largerchamber 44. The lamp 41 has an electrical lead or conductor 49 connectedthrough an electrical adapter socket 50 on the signal control unit Awith a conductor 5I of the switch mechanism contact 52. Lamps 48 and 48ahave a common conductor 53 similarly connected with a conduetor 54 ofthe switch mechanism contact 55. As shown in Figure 2, contacts 52 and55 are fixed in the body portion 2 in vertically spaced relation onrelatively opposite sides of one end of the switch arm 2U. The switcharm is pivotally supported at its other end on a post or pedestal 56 formovement vertically between the contacts and is provided with aconductor 5l and condenser 58 for connection through the adapter socket50 and conductor 59 with the aircraft engine ignition circuit.

A typical fuel system with the above described fuel flow warning deviceinstalled therein is shown in Figure 4. The system, alnrt from theincorporation of the subject invention therein, comprises main andauxiliary fuel tanks SII and 5I with fuel outlet tubes 50a and ila to aselector valve 52. The fuel line from the selector valve t0 theengine-driven main fuel pump 53 and hand-operated booster pump 64 isindicated at 65 and includes the strainer 66. The outlets of the pumpsare connected through a common fuel delivery tube 61 to the carburetorfuel inlet 68.

The carburetor 69 is shown provided with an air scoop or-ramming airintake 10 and a throttle 1|. A supercharger 12 is located in theinduction system between the carburetor and the engine intake manifold13. The conventional pump 63 is designed to deliver much more fuel atany speed than the engine actually requires, the surplus fuel beingrelieved. to the intake side of the pump by the automatic action of adifferential pressure operated relief valve of the well-knownbellows ordiaphragm type vented on one sideto the fuel pressure and on the otherside to the carburetor air intake pressure. The relief valve, shownconventionally at 14 with air vent line 15 to the carburetor impact tube18, by its balancing action helps rto maintain constant pump dischargepressure regardless of variations in pressure on the suction side of thepump. The conventional differential pressure gage for indicating thedifference between the air-pressure at the carburetor air inlet and thefuel pressure entering the carburetor is shown at 11 with its airconnection 18 vented to the carburetor air intake through vent line 19and impact tube 1G, and its fuel connection 80 connected to thecarburetor fuel inlet 68 by a fuelvent line 8|.

The conventional fuel pressure warning signal comprises a red signallamp 82 and the signal switch 83 in circuit connection with a source ofpotential 84 and a cut-out switch 85; the signal lamp being'conveniently located in the pilots compartment and the signal switchbeing installed close to the carburetor. The signal switch is adifferential pressure operated type vented to fuel pressure on one sidethrough the fuel connection 86 with the fuel vent line 8| and tocarburetor air pressure on'the other side through the air connection 81with the air vent line 18. During normal engine operation the fuelpressure is sufficiently high to keep the signal switch 83 open so thatthe lamp 82 is unlighted. Upon a serious loss or drop in fuel pressurethe signal switch closes and lights the lamp in warning to the pilot oflow-fuel pressure. Since operation of the fuel pressure warning signalis required only during engine operation it is generally connected inthe engine ignition circuit with the conventional storage battery as thesource of potential 84 and the presently employed ignition switch as thecut-out switch 85.

In installing the fuel flow warning device in the conventional fuelsystem, the signal control unit A is located in the fuel line on theintake side of the fuel pump, preferably between the bellows I producesa force acting downwardly through the spring 2| upon the switch arm 20.Movement of the fuel through the impeller chamber of the unit A in thenormal direction of flow selector valve 62 and the strainer 66. with theswitch arm conductor 59 connected as a branch lead with the ignitionswitch point 88. The signal unit B is mounted in the pilots compartmenton the instrument panel or otherwise conspicuously located in thevicinity of the pilot. Chamber of the unit A is connected to the impacttube 16 through vent tubes 89 and 19 and registers the carburetor airintake or scoop pressure. Chamber I2 is connected by a vent tube 9D withthe throat of a Venturi tube `9| in the direct air flow of the engineinduction system and registers Venturi suction. In normal engineoperation, the new volume of fuel should be at a predetermined valuecorresponding to the mass air flow at the carburetor for each engineoperating condition. v

The pressure difference between chambers and tends to displace theimpeller clockwise about its axis for producing a force which is ameasure of the fuel flow. This force is applied to the switch armthrough the medium of the shaft 29 and cam 3| in opposition to the forceproduced by the pressure differential between chambers and I2 andapplied to the switcharm in the manner hereinbefore described. g

The adjustment and calibration ofthe signalcontrol unit A is such thatthe impeller, switch arm, and associated parts are caused to assumedifferent given positions according to whether the fuel flow is normal,subnormal, or abnormal. The normal position is represented by the dottedline construction P of Figures. 5 and 6 and is assumed when the fuelsystem is operating normally, as when the fuel ow corresponds to theconsumption requirements of the engine. In this condition of fuel systemoperation, the opposing forces on the switch arm 20 hold the lattercentered between, and hence in open eircuit position relative to, thecontacts 52 and 55; the impeller 24 being in flow-sustained attitudesubstantially midway of the upper and lower limits of the travel withthe vvalve 40 in unseated relation to the impeller fuel ports 38. Thesignal lamps 41, 48 and 48a are unlighted because of the `break incircuit at the signalY control unit switch.

The subnormal or "No flow position is represented by the full lineconstruction Px of Figure 5 and is assumed when 'the flow of fuel ceasesor drops below the required rate. Such a condition may be encountered,during engine operation, as a result of restriction or exhaustion of thefuel between the supply source and the fuel pump, failure in thecarburetor, or irregular fuel flow. Figure 5 illustrates a condition ofsubnormal fuel fiow due to the lack of adequate fuel supply. The fuel inthe part of the system from the fuel tank to the fuel pump contains airand the flow is low and erratic, being pulsating rather than uniform; acommon occurrence when the quantity of fuel in the fuel tank isinsufficient to maintain uniform flow, particu-4 larly when the aircraftis operated-in vattitudes which prevent or retard fuel flow. Erraticfuel flow from the fuel tank to the inlet of the fuel pump most alwaysis encountered prior to the exhaustion of the fuel system ormalfunctioning of the high pressure side of system between the fuel pumpand the carburetor. This condition of low and erratic fuel now is notimmediately reflected in the high pressure side of the fuel systembecause of the operating characteristics of the conventional fuel pumpwhereby normal operating fuel pressure is maintained in the discharge orhigh pressure side of the fuel system for a considerable period afterthe fuel flow in the low pressure side of the system has dropped to anunsafe value. Hence, during this period of malfunction the conventionalfuel pressure gauge and the fuel drop warning device continue toindicate normal operating fuel pressure indicative of safe engine andfuel system operating conditions. With the fuel flow warn-l ing deviceof the present invention installed in the system as shown and described,it is obvious that decreased fuel flow between the tank and the fuelpump will decrease the fuel flow pressure against the impeller 24 withresultant lessening of the upward force applied to the underside of theswitch arm 20 through the medium of the impeller shaft 29 and cam 3l. Asa result of the unbalancing of the opposed forces, with the downwardforce predominating, the switch arm is forced downward into engagementwith the electrical contact 52 with consequent" closing of the circuitto the remotely located signal lamp 41 and illumination of the latter torender a No flow warning to the pilot. The downward movement of theswitch Aarm results in a counter clockwise movement of the cam 3l, shaft29, and impeller 24 from the normal position P to the No flow positionPx. It should be noted that at this particular time the fuel pressuregauge 11 and the unlighted drop warning lamp 82 are recording a normalcondition of fuel system operation. When the condition of decreased flowis remedied, as by switching the selector valve 62 to another fuel tankor taking otherf'corrective action to restore the fuel flow to therequired normal value, the switch mechanism is restoredl to position Pand the No flow warning lamp is extinguished indicating resumption ofnormal operation of the fuel system.

The abnormal or Excessive flow position is represented by the full lineconstruction Py of Figure 6 and is assumed when the flow of fuel exceedsthe required fuel consumption of the engine. Such a condition commonlyoccurs when leakage at a section or connection of the tubing on thepressure side of the fuel system results in loss of fuel to the externalarea, as indicated at y in Figure 6. The fuel loss to the carburetor iscompensated by an increase in the fuel flow and fuel volume output ofthe fuel pump as long as the fuel supply is adequate; the capacity ofthe fuel pump 63 being 'much greater than the maximum engine consumptionand is regulated by the relief valve 14 to maintain the correct fuelpressure value. Hence, during theoccurrence of such a condition ormalfunctioning of the system, the conventional fuel pressure guage andfuel drop warning device continue to indicate normal operating fuelpressure indicative of safe engine and fuel system operating conditionsalthough actually a serious fire hazard is present. Timely warning ofsuch a hazardous condition is afforded however, by the incorporationinto the fuel system of the warning device of the subject inventionwhich is responsive to variations in fuel flow rather than variations infuel pressure. Acceleration in fuel flow resulting from increased pumpaction due to malfunctioning of the system increases the upward pressureor force exerted against the underside of switch arm 2li through themedium of the impeller shafts 2t and Si. As a result of the unbalancingof the opposed forces, with the upward force predominating, a clockwisemovement of the impeller 2t shaft 29 and cam 3l occurs until theExcessive ow position Py is reached, at which time the switch armengages the electrical contact and closes the circuit to the lamps 48and 48a with consequent illumination of the lamps to render a warning 0fExcessive flow to the pilot. When, by corrective action with resultantdecrease in fuel flow, the proper balance between the opposed forces isrestored in conformity with the fuel consumption requirements of theengine, as measured or guaged by the pressure difference between thechambers I I and l2, the switch mechanism is activated to normalposition P and the Excessive flow lamps are extinguished in indicationof normal operation of the fuel system.

The fuel flow warning device, being responsive to fuel flow conditions,will render signal indications substantially immediately upon theoccurrence of a fuel flow which is disproportionate to requirements ofthe system for normal engine operation. Hence, it affords a correctionperiod of greater duration prior to engine failure than is afforded bythe conventional fuel pressure gauge 11 and fuel drop warning signal 82which are responsive to variations in fuel pressure rather than fuelflow. As previously pointed out herein, such undesirable ow conditionsmay exist for some time without drop in fuel pressure and, thereforewithout indication thereof either by the fuel pressure guage or the fueldrop warning signal. The fuel flow warning device is not intended toeliminate the fuel pressure guage or the fuel pressure drop warningsignal but to provide a supplementary warning device contributing togreater safety in aircraft engine operation. It can be readily adaptedto pressure types of fuel systems for aircraft without major alterationsto the fuel system and is designed to be constructionally andoperationally fool proof and free from malfunctioning within the limitsof possibility. The switch mechanism operates under a negative pressureafforded by Venturi suction which eliminates possibilities of moisturecondensation and electrical arcing, The free and valve-controlled fuelports in the impeller assure proper fuel flow should the impeller becomejammed or stuck in the flow passage from any condition ofmalfunctioning. A double pole, test switch S, shown in Figure 4, may lbeconnected in the fuel flow switch signal circuits for testing purposes,if desired.

Although the fuel flow warning device is herein shown and described asaffording immediate warning signal to the pilot through means of anelectrical circuit and lamps, the same objective may be attained by theuse of an auditory signal. It is to be understood, therefore, thatalterations and changes in the construction of the device, and thesubstitution of equivalents, may be made without departing from thespirit and scope of the inventions as set forth in the appended claims.

Having thus described the invention, we claim:

l. A fuel flow warning device for an engine fuel feed system, comprisingopposed pressure responsive means one of which is connected in the highpressure side of the system to be operated thereby for exerting a forceproportional to the instant fuel consumption of the engine and the otherof which is in communication with the low pressure side of the system tobe operated thereby for exerting a force proportional to the fuel flow,and a signalling circuit including a switch operatively connected withthe said opposed force exerting means to be maintained thereby incircuit-open position when the opposed forces are in balancedrelationship and to be moved into circuit-closed position when theopposed forces are in unbalanced relationship.

2. In a fuel system, a carburetor, a fuel source, a fuel feed lineconnecting the fuel source with the carburetor and including a fuel feedpump, opposed force-exerting means one of which is operatively connectedwith the carburetor to exert a force which is a function of the air flowthrough the carburetor and the other of which is operatively connectedto the fuel line between the pump and the fuel source to exert a forcewhich is a function of the fuel flow between the pump and of the switcharm and on relatively opposite side of the latter, a pressure-sensitivebellows within the chamber and having a pressure inlet externally of thechamber for the transmission of pressure to the interior of the bellows,a force-transmitting spring connecting the bellows and the switch arm, ashaft journaled in the housing and extending orosswise of the flowpassage, an impeller fixedly connected with the shaft and depending intothe flow passage, and a cam fixed on the shaft and engaging the switcharm in opposition to the said spring.

4. A fuel flow warning system having in combination a fuel consumingdevice, means for feeding fuel to the device, force-exerting meansconnected with the device and operable thereby in accordance with therate of fuel consumed by the device for producing a variable force whichis proportional to the rate of fuel consumption and which is a measureof the required rate of fuel flow to the device, force exerting meansvconnected with the fuel feeding means and operable thereby inaccordance with the rate of fuel flow therethrough for producing avariable force proportional to the rate of fuel flow, the twoforceexerting means being in relatively opposed relation for effecting aresultant force which corresponds to the instantaneous relation of thefuel ow through the fuel feeding means and the fuel consumed by thedevice, and means responsive to the said resultant force for visibly andcontinuously indicating said instantaneous relation.

5. In an engine fuel feed system, the combination of a source of fuelsupply, an engine induction housing, a fuel pump having an intakeconnection with the fuel supply source and a delivery connection withthe induction housing, opposed force-exerting means; one of which is apressuresensitive element vented to induction housing impact pressure onone side and to induction housing velocity pressure on the other side toexert a force proportional to the engine consumption and the other ofwhich is a ow responsive member operatively connected with the intakeside of the pump and operable to exert a force proportional to the fuelflow on one side of the pump, and a signalling circuit including acontrol switch connected to and operated by the said opposedforceexerting means to be maintained in circuit-open position when theopposed forces are in equilibrium and to be moved into circuit-closedposition whenever said forces are in unbalanced relationship.

6. In a fuel system, a carburetor, a fuel source, a fuel feed pumpconnected between the carburetor and the fuel source, a pair ofelectrical signalling circuits including a common control switch movablefrom an open circuit position in one direction to close one of thecircuits and in the opposite direction to close the companion circuit,and opposed force-exerting pressure-responsive means connected with theswitch and operable when equal to hold the switch in circuitopenposition, one of said means being responsive to the pressure differencebetween Venturi suction and impact pressure resulting from air flowthrough the carburetor to exert a force proportional to said airflow andtending to move the switch to close one of the circuits and the othermeans being responsive to fuel flow on the intake side of the pump toexert a force proportional to the fuel flow between the pump and thefuel source and tending to move the switch to close the other circuitwhereby an unbalance between the opposed forces results in the closingof a signal circuit.

7. A fuel feed system including a carburetor having an air flow passageprovided with a Venturi suction region and an impact pressure region, afuel source, a fuel pump having an intake connection with the fuelsource and a delivery connection with the carburetor, opposedpressureresponsive means one of which is vented to the carburetorVenturi suction on one side and to the carburetor impact pressure on theother side for exerting a force proportional to the pressuredifferential between the carburetor suction and impact pressure and theother of which is in communication with the intake side of the pump forexerting a force proportional to the fuel flow between the pump and thefuelsource, and fuel flow indicating means including a movable memberoperatively connected between the opposed forceexerting means to bemaintained in a given position when the opposed forces are equal and tobe deflected to positions at relatively opposite sides of the givenposition when there is an unbalanced relationship between the saidforces.

8. An engine fuel feed system including a carburetor, a. fuel source, afuel feed line connecting the fuel source with the carburetor andincluding a fuel feed pump, opposed force-exerting means one of saidmeans being a differential pressureresponsive member connected with thecarburetor other of said means being a pressure-responsive memberconnected to the fuel line between the pump and the fuel source andresponsive to the fuel flow therein for exerting a force which is ameasure of the fuel flow to the pump, and fuel flow indicator meansincluding a movable member operatively connected with the opposed forceexerting means to be maintained when the opposed forces are equal in agiven position indicative of a normal fuel flow and to be deflected topositions at relatively opposite sides of the given position inaccordance with an unbalanced relationship between the forces resultingfrom supernormal or subnormal fuel flow.

9. In an engine fuel system. an induction housing having a Venturi airpassage and an air impact pressure tube, a fuel source, a fuel pumphaving its intake connected with the fuel source and its outletconnected with the housing, a suction chamber connected with the Venturipassage, a pressure chamber connected with the irnpact tube, apressure-sensitive force-exerting device vented to the suction chamberon one side and tothe pressure chamber on the other side for exerting aforce proportional to the pressure differential between the suction andimpact pressures, a flow-responsive force-exerting device operativelyassociated with the intake side of the pump for exerting a forceproportional to the fuel v flow from the fuel source to the pump, and apair 11 12 of electrical signaling circuits including a. common controlswitch movable from a circuit open REFERENCES CITED position in onedirection to close one circuit and Th in the opposite direction to closethe other circuit' e following references are of record in the saidswitch being operatively associated with the me of this patent: saidforces-exerting devices to be acted on oppositely by said deviceswhereby it win be posimmm BTAIES PATENTS tioned in circuit open positionwhen the opposed Number Name Date forces are equal and moved to closeone or the 534,631 Carpenter Feb. 26, 1895 other of the circuits inaccordance with an un-` 1g` 1,533,530 `Wheatley et ar Apr. 14, 1925balance between the opposed forces.

JESSE VOLIAZZO.

VINCENT MEDVECKUS.

